1 . Field of the Invention
The present invention relates to optical elements, and more particularly to switchable holographic elements for use in imaging and display systems.
2. Description of the Relevant Art
Imaging and display systems are well known in the art. Imaging and display systems are often employed as, for example, night vision systems for military and avionic applications (i.e., wearable night vision devices combining infrared imagery with displayed symbology), camcorder view finders, telepresence (or augmented reality) and ultraviolet sensitive systems for document security applications. In essence, the systems operate by sensing image light from an external scene using, for example, an array of light detectors. The sensed light is converted by the detectors into corresponding electrical signals which in turn are processed on a frame by frame basis to remove artifacts or otherwise improve signal quality. The processed signals are ultimately provided to a light source which generates display light in accordance thereto for subsequent viewing by a user.
Many prior art imaging and display systems employ optical systems that include conventional optical components, such as glass lenses to focus image light onto an array of light detectors. Conventional optical components tend to be large, bulky, and complex. As a result, typical optical systems employing conventional optical components tend to be large, bulky, and complex. The complexity and size of prior art imaging and display systems open times is directly related to the number of optical elements employed therein. For example, night vision systems may employ an optical system having separate optical elements optimized for different bands of wavelength or different magnifications. One optical element in night vision systems may be employed to focus infrared image light while another optical element is employed to focus monochrome display light. Conflicting field of view requirements also contribute to the size and complexity of prior art imaging and display systems. Further, the radically different requirements between imaging and display systems generally requires optical systems contained therein to be radically different.
The problems outlined above are in large part solved by an optical system having at least first and second optical elements aligned on a common axis. In one embodiment, each of the first and second optical elements can operate in an active state or in inactive state and are formed from a polymer dispersed liquid crystal material. Each of the first and second optical elements is configured to transmit incident light substantially unaltered when each of the first and second optical elements operates in the inactive state. In the active state, however, each of the first and second optical elements does not transmit incident light substantially unaltered. Rather each of the first and second optical elements substantially alters light incident thereon when each of the first and second optical elements operates in the active state.
In one embodiment, the first optical element operating in the active state alters light incident thereon by converging it to a focal surface in space. Additionally, the first optical element may operate in the active state to alter incident light thereon by passing only a select wavelength band thereof. In one embodiment, the second optical element may have the same properties as the first optical element. Alternatively, the second optical element may have different properties so that in the active state, the second optical element substantially alters incident light thereon by reflecting it. Additionally, the second optical element may operate in the active state to substantially alter light incident thereon by reflecting a select wavelength band thereof.
The first and second optical elements in one embodiment are selectively coupled to a voltage source. In this embodiment, the first optical element operates in the inactive state and transmits light substantially unaltered when the first optical element is coupled to a voltage source. In contrast, when the first optical element is decoupled to the voltage source, the first optical element operates in the active state and substantially alters light incident thereon. In this embodiment, the second optical element when coupled to the voltage source operates in the inactive state and simply transmits light incident thereon substantially unaltered. In contrast, when the second optical element is decoupled from the voltage source, the second optical element operates in the active state and acts to substantially light incident thereon. Thus, it can be said that when the first and second optical elements are decoupled from the voltage source, the first and second optical elements operate substantially similar to conventional optical elements. However, when the first and second optical elements are decoupled from the voltage source, their optical properties (passing selecting bandwidths of light, converging light incident thereon, etc.) are erased.
The optical system set forth above may be employed in an imaging and display system including a sensor array, a first processing circuit for processing signals generated by the sensor array, and a light source for generating display light in accordance with signals output by the first processing circuit. In one embodiment, the first optical element operating in the active state converges light incident thereon. This converged light transmits through the second optical element unaltered when the second optical element is in the inactive state. The sensor array receives the converged light and generates a plurality of signals representative thereof. These signals are provided to the first processing circuit where there are processed, for example, to remove noise components therein. The process signals are subsequently provided to the light source which, in turn, generates display light in response thereto. This display light may be provided to the second optical element where it is reflected for viewing by a user of the system after being transmitted substantially unaltered through the first optical element operating in the inactive state.